In recent years, it has become increasingly common for companies and other such organisations to back-up their computing systems (and other in-house back-up systems) by storing data on a series of magnetic tape cartridges, for retrieval in the event that the data is lost or corrupted in the primary systems.
It will be appreciated that it is essential that such back-up data is accurately and completely stored and, in many systems, the integrity/accuracy of the data recorded to a magnetic tape cartridge or the like is checked by reading back data from the tape cartridge, checking the data read back for errors, and rewriting to the tape cartridge any data found to contain such errors. In fact, an industrial format has been defied for this type of transfer and storage system, in which it is stated that, if a block of data is read back containing one byte in error, it must be rewritten. However, such a strict requirement results in a lot of unnecessary wastage of tape due to excessive rewriting of blocks of data in the presence of random bit errors. Further, such unnecessary rewrites result in the transfer and storage of data taking an excessive amount of time.
We have devised an arrangement which overcomes these problems and provides a method and apparatus for effective and efficient data back-up.